Atomic Mass (mass number)- The average of all the masses of the naturally occurring isotopes of an element. The mass number is the rounded atomic mass. It is the number of protons and neutrons found in an atom. Isotope- Every existing type of element with a different number of electrons and neutrons. Atomic Number- The number of protons in the nucleus of an atom.
Quantum Theory-
This theory replaced Bohr because his energy levels only worked for Hydrogen.
The quantum theory uses complex mathematical equations to describe waves.
The model predicts quantized energy levels of electrons. It depends on the probability of finding an electron in a certain position.
This categorized the 7 energy levels into 4 orbitals.
Orbitals-
Area where an electron can be found.
There are 4 orbitals: s, p, d & f.
The orbitals are filled based on the location of the electrons on the periodic table.
S-Orbitals-
Given a 3-D figure, the s-orbital would look like a sphere.
It can hold a maximum of 2 electrons - one pair of electrons.
S-orbitals will occur in all 7 energy levels.
P-Orbitals-
Electrons begin filling the p-orbitals in the 2nd energy level after filling the 2s-orbital.
It can hold a total of 6 electrons - 3 electron pairs.
The shape of each of the p-orbitals look like a dumbbell.
D-Orbitals-
Electrons begin filling the d-orbitals in the 3rd energy level, after filling the 4s-orbital.
The orbitals will hold 10 electrons, 5 electron pairs.
The 3-D shape of the d-orbital is 4 x-shapes with a life-saver around the center.
F-Orbital-
They occur in the 4th energy level after filling the 6s-orbital.
The f-orbitals can hold 14 electrons - 7 electron pairs.
The electrons are in such chaos that there is no set shape to describe them.
Electron configurations-
A visual way to write how the electrons fill the orbitals.
The orbitals fill as you flow left-right and top to bottom on the periodic table: 1s, 2s, 2p, 3s, 3p, 4s, 3d, 4p, etc.
Use of Bohr's Model
Whens Bohr's model only worked for the Hydrogen atom, his energy ideas are still used.
Electrons are in energy levels and can move energy levels when the electrons become energized (quantized).
Bohr proposed the electrons can only reside in an energy level.
The lowest energy level is closest to the nucleus. Ground State- when electrons are in the lowest possible energy level. Quantum- amount of energy needed to jump energy levels (particular energies given) Excited State- when an electron has been quantized (given particular energy) - leads to waves of light. Calculations
E=hc/λ, v=c/ λ
E= energy (eV) or (Joules)
h= 6.63 x 10^-34 Joules/Hertz
c= 3.0 x 10^8 m/s
λ= wavelength (nm)
v= frequency (Hz = 1/sec) Sample Calculation
Calculate the frequency & energy of light waves that have a λ= 17.3 nanometers. What type of light wave is this?
(look on paper)
Trends in Periodic Table
When studying the periodic table one can tell many things about an element just by its location on the table. These trends help scientists identify new elements and understand why an element has different properties. Atomic Radius
Atomic radius within a group increases as one moves vertically down the periodic table.
Atomic radius within a period decreases as one moves horizontally right across the periodic table. Group - the column Period - the row Ionization Energy (the energy required to remove and electron from an element)
The energy required for elements within a group decreases as one moves vertically down the periodic table.
The energy required for elements within a period increases as one moves horizontally right across the periodic table. Shielding Effect
A decrease in the attraction of the outer electrons (valence electrons) to the positively-charged nucleus. Increases as one moves vertically down on the periodic table.
It remains constant as you move right across the periodic table because the electrons aren't being added to a new energy level. Electronegativity (EN)
How strong the bonds are within the compound. Decreases as you move down the periodic table because the energy levels are growing. Increases as you move right across the periodic table because more p+ are added to the nucleus allowing for more electrons. Electron Affinity
A measure of the energy change that occurs as an electron is added to an atom.
Has the same trends as electronegativity for the same reasons (what was wrote in previous section)
Atomic Mass (Mass Number)
The average of all the masses of naturally occurring isotopes of an element.
The mass number is the rounded atomic mass. It is the number of protons and neutrons found in an atom. Atomic mass is expressed in Atomic Mass Units (amu)
The mass number is the mass if both the protons and neutrons, not the total mass.
Scientists developed a unit to compare all atoms.
1 amu = 1.66 x 10^-24g (1/12th the mass of Carbon-12) Average Atomic Mass on the PT
When you read the mass on the PT, the units are amu
Cu = 63.55 amu
The average atomic masses are the average of the atomic masses of the isotopes occurring in nature.
Amu when a single atom; grams when larger amounts of materials. How to calculate the amu
Scientists use the percent of existence of isotopes multiplied by the mass all totaled to get the mass
Ex: Cu-63 exists 69.17% of the time yielding a mass of 62.94 amu and Cu-65 exists the other 30.83% of the time with a mass if 64.93 amu. Together they create the amu of Cu.
in s and p orbitals in that period, skip over d and f orbitals
groups of elements have the same number of valence electrons
group number is the same as the number of valence electrons
+ ion - group I = +1; group II = +2; group III = +3
max valence electrons, H and He are exception to octet rule (only 2 total)
ion - an element that has donated or taken electrons
+ions - Cations; located on left hand side of PT; groups I, II, and III (sometimes IV); give away some electrons; Ca+2: Calcium ion
-ions - Anions; located on the right hand side of PT; groups (sometimes IV), V, VI, VII; taking in electrons; O-2: oxide ion
Ionic Bonds
Oppositely charged ions attract and bond to each other. The compounds become known as salts.
Ex: The attraction of a Na+1 ion to a Cl-1 ion forms the compound commonly known as table salt - Sodium Chloride Writing Ionic Formulas
Write the cation and anion from the name:
Lithium Oxide: Li+1 O-2
Switch the charges to become subscripts
Li(sub2)O
Reduce if like charges or common multiples
(+2, -2 becomes 1:1, +4, -2 becomes 2:1) Determining Formulas Mathematically
Percent Composition
Calculating the percent that an element exists within a compound.
Essentially you're giving each element a grade on it's participation within a compound.
Sample: H2O
1. Mass of elements
a. H: 2*1.01 = 2.02 g
b. O: 1*15.99 = 15.99 g
2. Mass of compound
2.02 + 15.99 = 18.01 g
3a. Percent H: 2.02/18.01 = 0.112 x 100 = 11.2%
3b. Percent O: 15.99/18.01 = 0.8878 x 100 = 88.78%
If we have 12.31g of water after distillation, how many g of O are present?
12.31x.8878 = 10.9g O, which means 1.4 g of H
Working Backwards to get Formulas
We can also work backwards to determine the formula of a compound. This is called the empirical formula. It gives the lowest whole-number ratio of the elements in the compound.
When given a problem assume that you have 100g total (like percent, make it easy) 25.4% = 25.4g.
Calculate the moles of each element.
Divide the moles of each element by the smallest mole number to get the ratio (round to the nearest 0.5).
Multiply the ratio by 2 if you have a 0.5 ratio.
Write the formula using the whole number ratio.
Sample Problem
A compound is analyzed and found to a certain 25.9% N and 74.1% O. What is the empirical formula of the compound?
25.9g N x (1 mol N/14.0g) = 1.85 moles of N
74.1g O x (1 mol O/15.99g) = 4.63 moles of O
Ratio: 1.85/1.85:4.63/1.85 = 1:2.5
Whole Number 2(1:2.5) = 2:5
Formula N(2)O(5)
Naming Covalent Bonds
1) Elements are listed by lower group first.
2) If both elements are in the same group, the lower atomic number element is the first to bond.
3) 2nd element will end with -ide
4) Prefixes are used to tell how many atoms are in the bond (mono, bi, tri, etc.)
5) First element will only have a prefix if it is more than one.
Ex. BF(3) - Boron trifluoride
Dinitrogen pentaoxide - N(2)O(5)
Chemical Reactions
Introduction
Chemical reactions occur when bonds between the outermost parts of atoms are formed or broken
Chemical reactions involve changes in matter, the making of new materials with new properties, and energy changes.
Symbols represent elements, formulas describe compounds, chemical equations describe chemical reactions.
Chemical Equations
Their job: Depict the kind of reactants and products and their relative amounts in a reaction.
4 Al (s) + 3 O(2) (g) --> 2 Al(2)O(3) (s)
The number in the front are called the stoichiometric coefficients
The letters (s), (g), and (l) are the physical states of compounds. Parts of a Reaction Equation
Chemical equations show the conversion of the reactants (the molecules shown on the left of the arrow) into products (the molecules shown on the right of the arrow).
A + sign separates molecules on the same side
The arrow is read as "yields"
Example: C = O(2) --> CO(2)
This reads "carbon plus oxygen react to yield carbon dioxide"
Because of the principle of the conservation of mass (Lavoisier), an equation must be balanced. It must have the same number of atoms of the same kind on both sides. Symbols used in Equations
solid - (s)
liquid - (l)
gas - (g)
Aqueous solution - (aq)
Catalyst - ------->
Escaping gas - ( )
Change of temperature - ( )
Balancing Equations
When balancing a chemical reaction you may add coefficients in front of the compounds to balance the reaction, you may NOT change the subscripts.
Changing the subscripts changes the compound. Subscripts are determined by the valence electrons (charges for ionic or sharing for covalent)
Steps to Balancing Equations
There are four basic steps to balancing a chemical equation.
Write the correct formula for the reactants and the products.
Find the number of atoms for each element on the left side. Compare those against the number of the atoms of the same element on the right side.
Determine where to place coefficients in front of the formulas so that the left side has the same number of atoms as the right side for EACH element in order to balance the equation.
Check your answer to see if:
The numbers of the atoms on both sides of the equation are now balanced.
The coefficients are in the lowest possible whole number ratios. (reduced)
Some Suggestions to Help You
Take it one element at a time, working left to right except for H and O. Save H for next to last, and O until last.
IF everything balances except for O, and there is no way to balance O with a whole number, double all the coefficients and try again. (because O is a diatomic element)
(Shortcut) Polyatomic ions that appear on both sides of the equation should be balanced as independent units.
Isotope- Every existing type of element with a different number of electrons and neutrons.
Atomic Number- The number of protons in the nucleus of an atom.
Quantum Theory-
This theory replaced Bohr because his energy levels only worked for Hydrogen.
The quantum theory uses complex mathematical equations to describe waves.
The model predicts quantized energy levels of electrons. It depends on the probability of finding an electron in a certain position.
This categorized the 7 energy levels into 4 orbitals.
Orbitals-
Area where an electron can be found.
There are 4 orbitals: s, p, d & f.
The orbitals are filled based on the location of the electrons on the periodic table.
S-Orbitals-
Given a 3-D figure, the s-orbital would look like a sphere.
It can hold a maximum of 2 electrons - one pair of electrons.
S-orbitals will occur in all 7 energy levels.
P-Orbitals-
Electrons begin filling the p-orbitals in the 2nd energy level after filling the 2s-orbital.
It can hold a total of 6 electrons - 3 electron pairs.
The shape of each of the p-orbitals look like a dumbbell.
D-Orbitals-
Electrons begin filling the d-orbitals in the 3rd energy level, after filling the 4s-orbital.
The orbitals will hold 10 electrons, 5 electron pairs.
The 3-D shape of the d-orbital is 4 x-shapes with a life-saver around the center.
F-Orbital-
They occur in the 4th energy level after filling the 6s-orbital.
The f-orbitals can hold 14 electrons - 7 electron pairs.
The electrons are in such chaos that there is no set shape to describe them.
Electron configurations-
A visual way to write how the electrons fill the orbitals.
The orbitals fill as you flow left-right and top to bottom on the periodic table: 1s, 2s, 2p, 3s, 3p, 4s, 3d, 4p, etc.
Use of Bohr's Model
Whens Bohr's model only worked for the Hydrogen atom, his energy ideas are still used.
Electrons are in energy levels and can move energy levels when the electrons become energized (quantized).
Bohr proposed the electrons can only reside in an energy level.
The lowest energy level is closest to the nucleus.
Ground State- when electrons are in the lowest possible energy level.
Quantum- amount of energy needed to jump energy levels (particular energies given)
Excited State- when an electron has been quantized (given particular energy) - leads to waves of light.
Calculations
E=hc/λ, v=c/ λ
E= energy (eV) or (Joules)
h= 6.63 x 10^-34 Joules/Hertz
c= 3.0 x 10^8 m/s
λ= wavelength (nm)
v= frequency (Hz = 1/sec)
Sample Calculation
Calculate the frequency & energy of light waves that have a λ= 17.3 nanometers. What type of light wave is this?
(look on paper)
Trends in Periodic Table
When studying the periodic table one can tell many things about an element just by its location on the table. These trends help scientists identify new elements and understand why an element has different properties.
Atomic Radius
Atomic radius within a group increases as one moves vertically down the periodic table.
Atomic radius within a period decreases as one moves horizontally right across the periodic table.
Group - the column
Period - the row
Ionization Energy (the energy required to remove and electron from an element)
The energy required for elements within a group decreases as one moves vertically down the periodic table.
The energy required for elements within a period increases as one moves horizontally right across the periodic table.
Shielding Effect
A decrease in the attraction of the outer electrons (valence electrons) to the positively-charged nucleus.
Increases as one moves vertically down on the periodic table.
It remains constant as you move right across the periodic table because the electrons aren't being added to a new energy level.
Electronegativity (EN)
How strong the bonds are within the compound.
Decreases as you move down the periodic table because the energy levels are growing.
Increases as you move right across the periodic table because more p+ are added to the nucleus allowing for more electrons.
Electron Affinity
A measure of the energy change that occurs as an electron is added to an atom.
Has the same trends as electronegativity for the same reasons (what was wrote in previous section)
Atomic Mass (Mass Number)
The average of all the masses of naturally occurring isotopes of an element.
The mass number is the rounded atomic mass. It is the number of protons and neutrons found in an atom.
Atomic mass is expressed in Atomic Mass Units (amu)
The mass number is the mass if both the protons and neutrons, not the total mass.
Scientists developed a unit to compare all atoms.
1 amu = 1.66 x 10^-24g (1/12th the mass of Carbon-12)
Average Atomic Mass on the PT
When you read the mass on the PT, the units are amu
Cu = 63.55 amu
The average atomic masses are the average of the atomic masses of the isotopes occurring in nature.
Amu when a single atom; grams when larger amounts of materials.
How to calculate the amu
Scientists use the percent of existence of isotopes multiplied by the mass all totaled to get the mass
Ex: Cu-63 exists 69.17% of the time yielding a mass of 62.94 amu and Cu-65 exists the other 30.83% of the time with a mass if 64.93 amu. Together they create the amu of Cu.
(0.6917 x 62.94 amu) + (0.3083 x 64.93 amu)
63.55 amu.Conversion Factors ( | = fraction bar)
Avagadro's Number: 6.002x10^23 atoms/molecules | 1mole
Molar Mass: atomicmass(g) | 1mole
Valence Electrons
- in s and p orbitals in that period, skip over d and f orbitals
groups of elements have the same number of valence electronsgroup number is the same as the number of valence electrons
+ ion - group I = +1; group II = +2; group III = +3
max valence electrons, H and He are exception to octet rule (only 2 total)
ion - an element that has donated or taken electrons
+ions - Cations; located on left hand side of PT; groups I, II, and III (sometimes IV); give away some electrons; Ca+2: Calcium ion
-ions - Anions; located on the right hand side of PT; groups (sometimes IV), V, VI, VII; taking in electrons; O-2: oxide ion
Ionic Bonds
Oppositely charged ions attract and bond to each other. The compounds become known as salts.
Ex: The attraction of a Na+1 ion to a Cl-1 ion forms the compound commonly known as table salt - Sodium Chloride
Writing Ionic Formulas
Write the cation and anion from the name:
Lithium Oxide: Li+1 O-2
Switch the charges to become subscripts
Li(sub2)O
Reduce if like charges or common multiples
(+2, -2 becomes 1:1, +4, -2 becomes 2:1)
Determining Formulas Mathematically
Percent Composition
Calculating the percent that an element exists within a compound.
Essentially you're giving each element a grade on it's participation within a compound.
Sample: H2O
1. Mass of elements
a. H: 2*1.01 = 2.02 g
b. O: 1*15.99 = 15.99 g
2. Mass of compound
2.02 + 15.99 = 18.01 g
3a. Percent H: 2.02/18.01 = 0.112 x 100 = 11.2%
3b. Percent O: 15.99/18.01 = 0.8878 x 100 = 88.78%
If we have 12.31g of water after distillation, how many g of O are present?
12.31x.8878 = 10.9g O, which means 1.4 g of H
Working Backwards to get Formulas
We can also work backwards to determine the formula of a compound. This is called the empirical formula. It gives the lowest whole-number ratio of the elements in the compound.
- When given a problem assume that you have 100g total (like percent, make it easy) 25.4% = 25.4g.
- Calculate the moles of each element.
- Divide the moles of each element by the smallest mole number to get the ratio (round to the nearest 0.5).
- Multiply the ratio by 2 if you have a 0.5 ratio.
- Write the formula using the whole number ratio.
Sample ProblemA compound is analyzed and found to a certain 25.9% N and 74.1% O. What is the empirical formula of the compound?
25.9g N x (1 mol N/14.0g) = 1.85 moles of N
74.1g O x (1 mol O/15.99g) = 4.63 moles of O
Ratio: 1.85/1.85:4.63/1.85 = 1:2.5
Whole Number 2(1:2.5) = 2:5
Formula N(2)O(5)
Naming Covalent Bonds
1) Elements are listed by lower group first.
2) If both elements are in the same group, the lower atomic number element is the first to bond.
3) 2nd element will end with -ide
4) Prefixes are used to tell how many atoms are in the bond (mono, bi, tri, etc.)
5) First element will only have a prefix if it is more than one.
Ex. BF(3) - Boron trifluoride
Dinitrogen pentaoxide - N(2)O(5)
Chemical Reactions
Introduction
- Chemical reactions occur when bonds between the outermost parts of atoms are formed or broken
- Chemical reactions involve changes in matter, the making of new materials with new properties, and energy changes.
- Symbols represent elements, formulas describe compounds, chemical equations describe chemical reactions.
Chemical EquationsTheir job: Depict the kind of reactants and products and their relative amounts in a reaction.
4 Al (s) + 3 O(2) (g) --> 2 Al(2)O(3) (s)
The number in the front are called the stoichiometric coefficients
The letters (s), (g), and (l) are the physical states of compounds.
Parts of a Reaction Equation
- Chemical equations show the conversion of the reactants (the molecules shown on the left of the arrow) into products (the molecules shown on the right of the arrow).
- A + sign separates molecules on the same side
- The arrow is read as "yields"
- Example: C = O(2) --> CO(2)
- This reads "carbon plus oxygen react to yield carbon dioxide"
Because of the principle of the conservation of mass (Lavoisier), an equation must be balanced. It must have the same number of atoms of the same kind on both sides.Symbols used in Equations
- solid - (s)
- liquid - (l)
- gas - (g)
- Aqueous solution - (aq)
- Catalyst - ------->
- Escaping gas - ( )
- Change of temperature - ( )
Balancing Equations- When balancing a chemical reaction you may add coefficients in front of the compounds to balance the reaction, you may NOT change the subscripts.
- Changing the subscripts changes the compound. Subscripts are determined by the valence electrons (charges for ionic or sharing for covalent)
Steps to Balancing EquationsThere are four basic steps to balancing a chemical equation.
- Write the correct formula for the reactants and the products.
- Find the number of atoms for each element on the left side. Compare those against the number of the atoms of the same element on the right side.
- Determine where to place coefficients in front of the formulas so that the left side has the same number of atoms as the right side for EACH element in order to balance the equation.
- Check your answer to see if:
- The numbers of the atoms on both sides of the equation are now balanced.
- The coefficients are in the lowest possible whole number ratios. (reduced)
Some Suggestions to Help You